Overview

The Raymarine T121 is a wireless hull transmitter that converts connected depth, speed and compass transducer signals into Micronet wireless instrument data. It is used with Raymarine wireless instrument systems where hull sensor information needs to reach cockpit or mast displays without running instrument cabling through the boat.

The unit works from a 9 to 24V DC supply and has an internal lithium battery with up to 300 hours of standalone operation. It can also be kept charged from the boat’s DC system or with the optional T138 solar panel accessory, which is useful on racing sailboats and other installations where wiring runs need to stay simple.

For multihull installations, two hull transmitters and two sets of transducers can be fitted so the Micronet system can use wind information to determine which hull transducer is supplying the correct data. That keeps speed and depth data aligned with the active hull without adding manual selector switches.

Key features

• Converts depth, speed and compass transducer signals for use on Raymarine wireless Micronet instrument displays.
• Works with 9 to 24V DC boat power and includes an internal lithium battery for up to 300 hours of operation away from external power.
• Color-coded sensor connections help reduce wiring mistakes during installation near the transducers.
• Micronet wireless networking keeps instrument data moving without long cable runs between the hull sensor area and displays.
• Supports multihull setups where two transmitters and two transducer sets allow automatic hull source selection based on wind direction.
• Can be installed in a convenient onboard location, typically close to the connected transducers to keep sensor cable runs short.
• Compact housing measures 4.33 in W x 4.5 in H x 1.22 in D, helping it fit into tight instrument and bilge-adjacent spaces.

Installation and setup

This transmitter is normally mounted near the hull transducers so the speed, depth and compass connections stay organized and protected. The color-coded terminals make the wiring layout easier to follow, which matters when access is limited under berths, behind panels or inside lockers.

It should be placed where it is protected from avoidable impact and where cable strain can be controlled. On boats that already use Raymarine wireless instruments, it becomes the bridge between the wired transducers in the hull and the wireless display network above deck.

Compatibility and system use

This unit is for Raymarine wireless Micronet instrument systems. Depth, speed and compass transducers are required separately, so buyers should confirm the rest of the instrument package and existing sensors before replacing or adding a hull transmitter.

It is a practical fit for sailboats and performance multihulls that rely on accurate speed and depth data at the helm, in the cockpit or on mast displays, especially where reducing instrument cabling is part of the installation plan.

What’s included

• Hull transmitter